Enable forcing the usage of the static CRT in libffi's msvc wrapper

This is required for AddressSanitizer builds with clang-cl.

msvcc.sh

@@ -44,7 +44,8 @@
 
 args_orig=$@
 args="-nologo -W3"
-md=-MD
+static_crt=
+debug_crt=
 cl="cl"
 ml="ml"
 safeseh="-safeseh"
@@ -114,9 +115,14 @@ do
       defines="$defines $1"
       shift 1
     ;;
+    -DUSE_STATIC_RTL)
+      # Link against static CRT.
+      static_crt=1
+      shift 1
+    ;;
     -DUSE_DEBUG_RTL)
       # Link against debug CRT.
-      md=-MDd
+      debug_crt=1
       shift 1
     ;;
     -c)
@@ -211,6 +217,16 @@ if [ -n "$opt" ]; then
     args="$args -link -OPT:REF -OPT:ICF -INCREMENTAL:NO"
 fi
 
+if [ -n "$static_crt" ]; then
+    md=-MT
+else
+    md=-MD
+fi
+
+if [ -n "$debug_crt" ]; then
+    md="${md}d"
+fi
+
 if [ -n "$assembly" ]; then
     if [ -z "$outdir" ]; then
       outdir="."